In the previous (discussion)
741it has been established that,
at the beginning, dynasties are inevitably kind in the exercise of their
power and just in their administration. The reason is either their
religion, when (the dynasty) is based upon religious propaganda, or
their noble and benevolent attitude toward others, which is required by
the desert attitude that is natural to dynasties (at the beginning).

A
742kind and benevolent rule
serves as an incentive to the subjects and gives them energy for
cultural activities. (Civilization) will be abundant, and procreation
will be vigorous. All this takes place gradually. The effects will
become noticeable after one or two generations at best. At the end of
two generations, the dynasty approaches the limit of its natural life
743At that time, civilization has reached the
limit of its abundance and growth.

It should not be objected here that it was stated before
744 that in the
later (years) of a dynasty, there will be coercion of the subjects and
bad government. This is correct, but it does not contradict what we have
(just) said. Even though coercion makes its appearance at that time and
the revenues decrease, the destructive influences of this situation on
civilization will become noticeable only after some time, because things
in nature all have a gradual development.

In the later (years) of dynasties, famines and
pestilences become numerous. As far as famines are concerned, the reason
is that most people at that time refrain from cultivating the soil. For,
in the later (years) of dynasties, there occur attacks on property and
tax revenue and, through customs duties, on trading.745
Or, trouble occurs as the result of the unrest of the subjects and the
great number of rebels (who are provoked) by the senility of the dynasty
to rebel. Therefore, as a rule, little grain is stored. The grain and
harvest situation is not always good and stable from year to year. The
amount of rainfall in the world differs by nature. The rainfall may be
strong or weak, little or much. Grain, fruits, and (the amount of) milk
given by animals varies correspondingly. Still, for their food
requirements, people put their trust in what it is possible to store. If
nothing is stored, people must expect famines. The price of grain rises.
Indigent people are unable to buy any and perish. If for some years
nothing is stored, hunger will be general.

The large number of pestilences has its reason in the
large number of famines just mentioned. Or, it has its reason in the
many disturbances that result from the disintegration of the dynasty.
There is much unrest and bloodshed, and plagues occur. The principal
reason for the latter is the corruption of the air (climate) through
(too) large a civilization (population).746
It results from the putrefaction and the many evil moistures with which
(the air) has contact (in a dense civilization). Now, air nourishes the
animal spirit
747and is constantly with it.
When it is corrupted, corruption affects the temper of (the spirit). If
the corruption is strong, the lung is afflicted with disease. This
results in epidemics, which affect the lung in particular. (Even) if the
corruption is not strong or great, - putrefaction grows and multiplies
under (its influence), resulting in many fevers that affect the tempers,
and the bodies become sick and perish. The reason for the growth of
putrefaction and evil moistures is invariably a dense and abundant
civilization such as exists in the later (years) of a dynasty. (Such
civilization) is the result of the good government, the kindness, the
safety, and the light taxation that existed at the beginning of the
dynasty. This is obvious. Therefore, it has been clarified by science
748 in the proper
place that it is necessary to have empty spaces and waste regions
interspersed between civilized areas. This makes circulation of the air
possible. It removes the corruption and putrefaction affecting the air
after contact with living beings, and brings healthy air. This also is
the reason why pestilences occur much more frequently in densely settled
cities than elsewhere, as, for instance, in Cairo in the East and Fez in
the Maghrib.